1. Field of the Invention
The present invention relates to determining the center of gravity of objects, and, in particular, to methods and apparatuses for determining the three-axis center of gravity of packages on conveyor systems.
2. Statement of Related Art
In the field of package shipping, packages are gripped by automated handling systems to move packages from one location to another. In addition, in the field of package shipping, packages are stacked one upon the other into self-supporting walls of packages. In both the gripping and stacking of packages, knowledge of the location of the center of gravity of each package is important. In gripping by automated handling systems, the location of the center of gravity of a package determines the most stable grip position. In stacking of packages into self-supporting walls, the location of the center of gravity of a package determines the most stable placement position for that package in a stack with other packages.
In the field of package shipping, packages need to be moved and placed quickly, safely, and cheaply. As such, speed, accuracy, and cost are important criteria in determining the effectiveness of a system for measuring the center of gravity of a package in the field of package shipping. Better systems of measurement are those that can measure the center of gravity of packages with high accuracy in a short amount of time and at a low cost.
The location of the center of gravity of a package may be represented by three coordinates in the standard three-axis orthogonal cartesian coordinate system. This representation is known as the three-axis center of gravity. In this three-axis center of gravity representation, each coordinate represents the displacement of the center of gravity of the package along the corresponding axis of the cartesian coordinate system from some reference point, such as a selected corner of the package.
In known systems for the measurement of the location of the center of gravity of packages, each coordinate of the three-axis center of gravity is determined individually and separately. U.S. Pat. No. 2,782,631, issued to Baltrukonis et al. on Apr. 14, 1955, teaches a center of weight distribution locator for measuring the center of gravity of an object. This locator measures the location of the center of gravity of an object in one axis at a time.
In order to use the locator of Baltrukonis et al. to determine all three coordinates of the three-axis center of gravity of packages propelled along a conveyor system, it is necessary to remove each package from the conveyor system and measure each coordinate individually with the locator. This process requires removing the package from the package stream, placing the package on the locator to measure one coordinate of the center of gravity, rotating the package in the proper direction to measure a second coordinate, rotating the package a second time about a different axis to measure the third coordinate, and replacing the object onto the package stream. Such a process for determining the three-axis center of gravity using the locator of Baltrukonis et al. is time consuming and involves inefficient movement. In addition, the mechanism required to remove, rotate, and replace each package in order to measure automatically all three coordinates would be very expensive.
Thus, while the prior art does teach systems for measuring the three-axis center of gravity of packages, the slow speed and high cost of such systems make it ill suited for the field of package shipping. What is needed is a system for measuring the three-axis center of gravity of packages in a stream of packages without having to remove the packages from the stream and with minimal disruption of the flow of the package stream.